The present invention relates to an image transfer type image recording apparatus such as an electrophotographic copying apparatus, particularly to improvements on the image transfer-separation section.
As is generally known, in an image recording apparatus such as electrophotographic copying apparatus, image transfer paper (referred to as transfer paper, hereinafter) such as plain paper is fed onto an image bearing member (e.g., a photosensitive drum) on which a toner image is formed; said toner image is transferred onto the transfer paper by a transfer electrode device such as a corona discharging device as shown by FIG. 1 being positioned behind the image transfer paper. The transfer paper then is separated from the image support by a separation device (e.g., a separation roller, a stretched fixed belt of which a portion is in frictional contact with the surface of the photosensitive drum, or a combination of such means) which is adjacent to said transfer electrode device.
In an image transfer-separation section in which such methods are put into practice, it is desirable to construct said section so that the transfer paper may be conveyed as smoothly as possible. On the other hand, however, the compactness of the apparatus is requested nowadays from the view point of space-saving, necessitating that the diameter of the image support such as a photosensitive drum be minimized. To satisfy the latter requirement, the smaller the diameter of the image support with the other elements arranged to give full play to their normal function, the more it can not help arranging a forced conveyance path of transfer paper from the image transfer section through the separation section. For example, in a conventional apparatus using a roller as a separation means, the gap between the image transfer section and the separation section thereof is a distance of 30-40 mm.
The gap as described herein means the length of tangent line 100 (refer to FIG. 2) which touches the peripheries of both the drum and the separation roller, and which intersects the lines drawn from the center of the drum to the center of the transfer electrode and to the center of the separation roller, respectively.
Such being the case, when stiff paper such as paper having the weight of heavier than 70 kg, or curly paper is used as a transfer paper, the rear end of the transfer paper will not come into close contact with the image support, and consequently the defect of so-called poor transfer will be caused, that is, the efficiency of transfer will be lowered at the rear end of the transfer paper. A forced conveyance path of transfer paper also means that there is long period of contact time of the image support with an image transfer paper. Such being the case, it can cause such a defect that image quality will be lowered if there is any difference between the speeds of transfer of the paper conveyance and of the image support surface.
In such types of conventional electrostatic image recording apparatus, there has been a natural limitation to shorten the contact time of transfer paper by making the transfer electrode device closer to the separation device by their very design, because the corona discharger having a "U" shape sectional surface opposite and open to the image support is used as the transfer electrode device.